It's so variable though. Everyone has different incomes, different expectations, and kids have all sorts of different lifestyles.
I have DS(15) and DD(13), and both get £30 a month paid into their accounts.
I pay for school stuff, phone contracts, essential clothes and toiletries. They are expected to fund their own socialising, whatever birthday gifts they want to buy for friends, and any extra clothes they want.
DS is tighter than two coats of paint - every single penny of that monthly 30 quid has been saved for two years. He wouldn't dream of buying his mates a birthday present, isn't interested in buying clothes, and they never go to the cinema.
He's reasonably sociable - but he and his mates will meet at the park for a game of football or cricket, and DS will take a water bottle with him.
On the other hand, DD is very sociable. She loves meeting up with her friends at the weekend, and going into town. She's starting to get a bit of independence, and is allowed to take the bus into the bigger town 20 minutes away - which has Primark and New Look, so she's in heaven.
They'll often go to Starbucks for a drink, and will arrange to meet at the local cinema on a Saturday afternoon. They've also started going swimming at the Leisure Centre some Sunday afternoons for the fun inflatables sessions.
I've started giving DD some extra pocket money sometimes to cover her extra expenses. I'm aware that this might not be considered totally fair - however, if she runs out of money, then she can't join her friends having fun - and would just sit in her room on her laptop, so that doesn't feel right either?